Research could lead to better materials for body armor, medical implants

Below:

Next story in Science

Beards composed partly of iron help mussels hold onto rocks and ships, according to new research published today in the journal Science.

While this may sound all well and good for the mussels, the research could eventually lead to stronger, stretchier materials in a range of applications from body armor to medical implants using environmentally friendly processes.

"Engineers and nature both face the same kinds of physical pressures," said Matt Harrington, a scientist at the Max Planck Institute for Colloids and Interfaces in Germany and co-author of the study. "Nature has had the benefit of billions of years of evolution and experimentation to come up with the best solutions."

The researchers looked at two species of mussel, the California Mussel and the Mediterranean mussel, which have similar beards. Technically known as byssal threads, a mussel uses its beard to anchor itself to a particular rock, boat or pier.

When a mussel finds a place it likes, the two shells part slightly and a large, muscular organ known as the foot emerges. Within minutes, the foot has created a strong fiber roughly the width of a human hair and two to five centimeters (0.8 to 1.9 inches) long. When a mussel really doesn't want to move, the mollusk produces 50 to 100 byssal threads to anchor itself.

These threads are critical to the mussel's survival. Huge waves crash down regularly onto the small shelled creatures, blasting them with abrasive sand. If the byssal threads can't hold on, it will be swept away and likely killed or eaten.

Despite the enormous forces the mollusk is subjected to, the byssal fibers can stretch two times or more their length but rarely break, even after being pulled and relaxed thousands of times.

The manner in which these fibers are constructed is unique. About 95 percent of the inner layer of these fibers is composed of a smooth, stretchy material, while the outer layer is made up of collagen laced with iron. No other known material on Earth exhibits this kind of soft and stretchy inside, and hard, flexible and protective outside, said Holten-Anderson.

While this study helps to explain how the mussels' fibers work, the next step for the chemists is to create a synthetic version of the mollusk's beard, which could take years.

When, and if, researchers eventually do synthesize the beard, the resulting materials will be made in a more environmentally friendly way than most petroleum-based products. If a mussel can create incredibly strong and wear-resistant fibers in seconds at room temperature, in ambient pressure and without corrosive chemicals, then humans should be able to do the same.

One possible use for a synthetic version of byssal threads would be in body armor for soldiers and police. The byssal thread's flexible yet penetration-resistant properties could simultaneously protect soldiers while allowing them a freedom of movement current armor lacks.

The exact materials likely won't be the same, said Russell Stewart, a scientist at the University of Utah who also studies the physical properties of marine animals and was not involved in the Science study. However, the idea of a soft, stretchy center protected by a hard, extensible exterior could be adapted using existing materials.

Safer, longer-lasting medical implants could also result, since new materials developed from the mussels' fibers could help to anchor such devices in the human body. However, medical implants that borrow from these mussels are still a long way off, given the time and effort involved in producing, testing and approving such products for consumer use.

In the short-term, materials based on the mussels' fibers could be used to create a whole new generation of ropes and cords used in everything from mountain climbing to ship-rigging.

"Just knowing the physical structure of the byssal threads will be helpful," said Stewart. "The results of their research is pretty conclusive, and the work was very elegant. If we could mimic this material, it would have a lot of useful applications."